The main issue I see with 'Communities & Rewards' is that it always creates a situation where there you just have many joining the community only really for the rewards and not so much because they genuinely want to be part of a community. I tried to create a betting community way back but it just doesn't work.
A good example is that if tomorrow someone would start a community around carrots with enough voting power behind it, you all of a sudden will see a ton of people being 'passionate' creating content around carrots.
I guess, monetary reward motivation is the universal truth, I will not say it is a problem of Hive. Community content moderation can easily handle this.